This invention relates generally to hardness testers of the indentation type and, more particularly, to a device which is capable of testing the hardness of a nickel battery electrode and, more specifically, the hardness of electrode plaque.
Currently, more and more emphasis is being placed upon the development of high performance, compact, lightweight, miniaturized power sources. Such power sources generally are in the form of high-quality, nickel-cadium, nickel zinc, and nickel-hydrogen cells or batteries. Such batteries have many applications, although their primary application is in use as an aircraft emergency power source and/or spacecraft power source.
Historically, however, there has been little interest in the mechanical characteristics of the sintered battery electrode substrate material, more commonly referred to as electrode plaque or simply by the term plaque. This substrate (plaque) has been characterized primarily in terms of its chemical compatibility, porosity, current carrying capability and surface area. Plaque has commonly been viewed as merely an immobile and inert "container" for the active chemical components or chemically active electrode material.
Recently attention has been given by us to the fatigue characteristics of the electrode plaque, because fatigue has been shown to result in long term capacity degradation of nickel electrodes. An example of a battery electrode fatigue simulator can be found in U.S. patent application Ser. No. 227,565, filed by us on Jan. 22, 1981. In addition, we have investigated plaque hardness, and have found that hardness affects the short term capacity characteristics and utilization efficiency of electrodes. In essence, we have determined that the harder the plaque is, the poorer the electrode will perform. The effect of this conclusion is that it implies that the electromechanical process occurring is not independent of the substrate mechanical characteristics. This is particularly important in the Ni-H.sub.2 battery in which the life-limiting component of the battery is the nickel electrode. Consequently, the plaque configuration and mechanical properties (including hardness) must be engineered to obtain maximum efficiency and life from the nickel electrode.
Currently available hardness testing equipment, such as the Brinell and Rockwell testers are inadequate for electrode plaque hardness testing for a number of obvious reasons, including the thinness (i.e., 0.75 mm) of the normally used electrode plaque, and the non-homogenous, sintered structure of the electrode plaque.
It is, therefore, readily apparent that what is needed in the art, and is not currently available, is a device with which the relative hardness of the electrode plaque (and other very thin specimens of non-homogenous, sintered material) can be tested and ascertained for contemplated potential use of the particular electrode plaque (s), and additionally for use in the quality control of electrode plaques and other similar materials.